The disclosure of Japanese Patent Application No. HEI 11-369719 filed on Dec. 27, 1999 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to an evaporative emission control system that prevents fuel vapors in a vehicular fuel tank from being discharged into the atmosphere and, more particularly, to an evaporative emission control system that prevents fuel from being transferred to a canister through a vapor vent line when the fuel tank is filled up and prevents fuel from flowing out of the tank when the vehicle inclines or rolls over.
2. Discussion of Related Art
A vehicular fuel tank is provided with a liquid level sensing valve, a fuel cut valve and the like. The liquid level sensing valve is adapted to close a vapor vent line when the tank is filled up. The fuel cut valve is adapted to close an evaporation line to prevent fuel from flowing out of the line, for example, when the vehicle inclines or rolls over. Each of these valves includes a float that vertically moves in accordance with the liquid level of the fuel.
Hereinafter, one example of evaporative emission control systems as part of the related art will be described with reference to FIG. 1. A valve casing 4 incorporating a liquid level sensing valve 2 and a fuel cut valve 3 formed as a unit is mounted on the fuel tank 1. The valve casing 4 is composed of a lower valve casing 4A and an upper valve casing 4B disposed above the lower valve casing 4A. A liquid level sensing float 5 and a fuel cut float 6 are disposed in the lower valve casing 4A.
A valve portion 7 is provided on an upper surface of the liquid level sensing float 5. Also, a valve portion 8 is provided by an upper portion of the fuel cut float 6. Valve ports 9, 10 are formed between the lower valve casing 4A and the upper valve casing 4B. The valve port 9 is opened and closed by the valve portion 7, and the valve port 10 is opened and closed by the valve portion 8. The upper valve casing 4B is provided with a vent conduit 11, which communicates with the valve port 9 through a space 12. The space 12 also communicates with the valve port 10 through a conduit 13.
The operation of the evaporative emission control system of the related art shown in FIG. 1 will be now described.
If the pressure of fuel vapors in the fuel tank 1 becomes high during refueling, fuel vapors flow through the valve port 9 formed in the valve casing 4, and are discharged into a canister (not shown), an intake pipe (not shown) and the like through the vent conduit 11, as indicated by arrow P in FIG. 1.
If the liquid level of the fuel in the fuel tank 1 is elevated, the liquid level sensing float 5 rises and the valve body 7 closes the valve port 9. This prevents fuel from being directly fed to the canister.
If the pressure of fuel vapors in the fuel tank 1 remains high during normal operations, the liquid level sensing float 5 sticks to the valve port 9. In this case, since the vent conduit 11 remains closed, it is necessary to reduce the pressure in the fuel tank 1. To this end, the pressure is released through the valve port of the fuel cut valve 23 so that the liquid level sensing float falls because of its own weight.
If the vehicle inclines by a large degree or rolls over, a large amount of fuel in the fuel tank 1 may flow towards the canister through the valve port 10 and the conduit 13. However, when the vehicle inclines by a large degree or rolls over, the fuel cut float 6 rises and the valve body 8 closes the valve port 10, whereby fuel is prevented from flowing out.
In the aforementioned structure as shown in FIG. 1, the liquid level sensing float 5 and the fuel cut float 6 are disposed in the same valve casing 4. However, other structures are also known in which the liquid level sensing float and the fuel cut float are individually disposed in separate valve casings.
Another example of evaporative emission control systems as part of the related art will be described with reference to FIG. 2. A liquid level sensing valve 22 and a fuel cut valve 23 are separately mounted on a fuel tank 21. A valve casing 24 of the liquid level sensing valve 22 is formed with a vent conduit 25, and a valve casing 26 of the fuel cut valve 23 is formed with a conduit 27. A space 28 is formed in the valve casing 24 of the liquid level sensing valve 22. A connection port 29 that extends from the space 28 is connected to the conduit 27 by means of a hose 30.
The example shown in FIG. 2 also performs substantially the same operation as the example shown in FIG. 1. That is, if the liquid level of fuel in the fuel tank 21 becomes high, the liquid level sensing valve 22 closes the vent conduit 25. This prevents fuel from being directly fed to the canister and the like.
If the pressure of fuel vapors in the fuel tank 21 remains high during normal operations, the float of the liquid level sensing valve 22 sticks to the valve port, and the vent conduit 25 remains closed. Therefore, it is necessary to reduce the pressure in the fuel tank 21. To this end, the pressure in the fuel tank 21 is released through the valve port of the fuel cut valve 23, so that the float of the liquid level sensing valve 22 falls because of its own weight.
If the vehicle inclines by a large extent or rolls over, a large amount of fuel in the fuel tank 21 may flow towards the canister through the valve port of the fuel cut valve 23 and the conduit 27. However, when the vehicle inclines by a large degree or rolls over, the float of the fuel cut valve 23 rises and the valve port is closed, whereby fuel is prevented from flowing out.
However, the aforementioned evaporative emission control systems as part of the related art have the following disadvantages.
First of all, since the space 12, 28 is directly connected to the vent conduit 11, 25 with no intervening member therebetween, the fuel that has leaked out from the valve port 9 due to vibration of the vehicle, or the like, may be transferred toward the canister and degrade the canister.
Furthermore, the valve port 9 may be directly exposed to the fuel in the fuel tank, and therefore the fuel is more likely to leak through the valve port 9.
With regard to the structure in which the connection port 29 of the liquid level sensing valve 22 and the conduit 27 of the fuel cut valve 23 are connected with each other by the hose 30, the connecting operation cannot be accomplished in a simple manner. It thus takes a lot of time and labor to provide the system as shown in FIG. 2, while requiring many types of parts or components.
It is thus an object of the invention to reduce or eliminate the disadvantages of the evaporative emission control systems as the related art, and to provide an evaporative emission control system that achieves reduction of the amount of leaking fuel, simplified procedure of mounting or connecting pipes, and reduction of the number of types of required parts or components.
To accomplish the above object, an evaporative emission control system is provided according to the present invention, which includes: an upper valve casing defining a vent conduit; a lower valve casing disposed under the upper valve casing; a float disposed within the lower valve casing, the float being vertically movable depending upon a liquid level of fuel in a fuel tank, the float including a valve portion that faces the upper valve casing; a valve port provided between the upper valve casing and the lower valve casing, the valve port being opened and closed by the valve portion of the float, the upper valve casing defining a space between the vent conduit and the valve port; and a flow restricting device disposed in the space of the upper valve casing so as to obstruct flow of fuel from the valve port to the vent conduit.
In one preferred form of the invention, the flow restricting device consists of a shield device that reduces a cross-sectional area of the space through which the valve port communicates with the vent conduit.
In another preferred form of the invention, the flow restricting device defines a helical passage in the space of the upper valve casing.
In a further preferred form of the invention, the flow restricting device consists of at least one partition wall that divides the space of the upper valve casing into two or more chambers that are arranged in a vertical direction. In this case, each of the partition walls has a through-hole formed therethrough.
The evaporative emission control system as described above may further include a cut valve having a vent port. In this system, the upper valve casing may be provided with a cut valve connection port that is open to the above-indicated space of the upper valve casing, and is connected to the vent port of the cut valve.